The American Cancer Society estimates that approximately 20,500 new cases of primary brain and nervous system tumors will develop and approximately 12,740 patients will die in the U.S. each year (Jemal et al., Cancer J. Clin., 57:43-66 (2007)) as a result of these cancers. Brain tumors account for approximately 85 to 90% of all central nervous system malignancies. Glioblastoma is the most aggressive and most common glioma accounting for 51% of all gliomas (CBTRUS 2008 Statistical Report: Primary Brain Tumors in the United States—CBTRUS, 2000-2004 (2008)). Despite advances in conventional treatments such as surgical resection, radiation therapy, and chemotherapy, the prognosis for gliomas, as well as other types of brain and nervous system cancer, may be poor. For example, most patients with glioblastoma multiforme (GBM) survive less than 15 months from diagnosis. Accordingly, there exists an unmet need for additional treatments for cancer, particularly gliomas.